Neublastin, also known as Artemin and Enovin, is a 24-kDa homodimeric secreted protein that promotes the survival of neurons of the peripheral and central nervous system such as dopaminergic neurons (Baudet et al., 2000, Development, 127:4335; Rosenblad et al., 2000, Mol. Cell Neurosci., 15(2):199; GenBank AF120274). The gene encoding neublastin has been cloned and sequenced (Roseblad et al., 2000, Mol. Cell Neurosci., 15(2):199; Baloh et al., Neuron, 21:1291).
Neublastin is a member of the glial cell line-derived neurotrophic factor (GDNF) ligand family. At the cellular level, GDNF members activate the receptor tyrosine kinase, RET. RET associates with a co-receptor, GDNF family receptor alpha (GFRalpha), a glycosylphosphatidyl inositol (GPI) linked membrane protein that provides ligand specificity for RET. Four GFRalphas are known (GFRalpha1-4). Neublastin binds to GFRalpha3 together with RET forming a ternary signaling complex (Baudet et al. 2000, Development, 127:4335; Baloh et al., 1998, Neuron, 21:1291), which is localized predominantly on nociceptive sensory neurons (Orozco et al., 2001, Eur. J. Neurosci., 13(11):2177). These neurons detect pain and injury. Thus, neublastin has clinical application in the general treatment of neuropathy and more specifically in the treatment of neuropathic pain.
Neublastin and the other GDNF family members are members of the transforming growth factor beta (TGF beta) superfamily and thus, are characterized by the presence of seven conserved cysteine residues with similar spacing which form the structure of a cysteine knot (Saarma, 1999, Microsc. Res. Tech., 45:292). Each monomer contains two disulfide bonds that form a closed loop structure encircling the third disulfide to form a tight knot structure. The seventh cysteine contained within each monomer forms an intermolecular disulfide bond, covalently linking the monomers to form the final dimer product (Rattenholl et al 2000, J. Mol. Biol., 305:523).
TGF beta family members are synthesized as pre pro proteins that eventually are secreted as a mature homodimer after cleavage of the signal peptide and pro-domain (see e.g. Rattenholl, et al., 2000, J. Mol. Biol., 305:523; Fairlie et al., 2001, J. Biol. Chem., 276(20): 16911). Both the signal peptide and pro-domain mediate proper secretion for TGF beta family members (Rattenholl et al., 2000, J. Mol. Biol., 305:523; Rattenholl et al., 2001, Eur. J. Biochem., 268:3296).